A 3.9 magnitude earthquake struck North Korea's northwestern province bordering China on Thursday, which is believed to be a natural one, the South Korean weather agency said.The quake struck an area 7 kilometers northeast-east of Ryongrim in Jagang Province, at 7:41 p.m., according to the Korea Meteorological Administration (KMA).The epicenter was at a latitude of 40.54 degrees north and a longitude of 126.75 degrees east, the KMA said.The quake is believed to have occurred naturally, it added.Source: Yonhap News Agency